Thanks for your answer. However I still do not get the whole picture.
Here is my understanding:
Let say I have copied some code, call it CODE-1, from network into memory.
Before I can execute CODE-1 , I need to flush the instruction cache,
which obviously does not contain CODE-1. By the way, CODE-1 is likely
to be present in D-Cache but this does not help so much.
When Instruction cache flush is performed, all the I-Cache lines are
invalidated to force the core to fetch from main memory instead of I-cache.
Let's call the routine performing this operation CODE-INV. If CODE-INV is
running cached, then it is contained in some cache lines that we will call
CODE-INV-LINES. CODE-INV is a loop that goes through all the cache lines and
mark them as invalid.
At some point of this process, CODE-INV-LINES are invalidated but as CODE-INV
goes on to the next lines, it is re-inserted into CODE-INV-LINES.
So when CODE-INV returns, all the I-Cache lines are marked Invalid except
Is this correct ?
If it is why is this not causing problems ? Since there is a chance that
CODE-1 contains code whose cache location is also CODE-INV-LINES
and thus gets wrong instructions.
From: Geert Uytterhoeven [mailto:firstname.lastname@example.org]
Sent: Freitag, 12. Juli 2002 11:27
To: Sedjai, Mohamed
Cc: Jon Burgess; Ralf Baechle; Gleb O. Raiko; Linux/MIPS Development;
Subject: RE: mips32_flush_cache routine corrupts CP0_STATUS with
On Fri, 12 Jul 2002, Sedjai, Mohamed wrote:
> If you run instruction cache flushing cached, then the cache will be dirty
> when the routine returns. At least the line(s) containing the routine itself ?
> Or am I missing something ?
Since the contents of the instruction cache are never changed (except by a
cache load), an instruction cache line can never become dirty.
Dirty cache lines and cache line write back are an exclusive privilege of write
back data caches.
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- email@example.com
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds